Industrial manufacturing facilities, for the most part, include plant regions or space functionally allocated to the performance of piece part machining and fabrication procedures. The traditional "machine shop" has been composed of a variety of machine tools which treat input stock to carry out such classic operations as turning, milling, drilling, grinding, forging, centering, stamping, heat treating, washing, and the like. Improved machine technology has significantly expanded machine shop capabilities and effectiveness for performing these operations, for example, numerically controlled devices have become commonplace and serve to somewhat automatically carry out a variety of machining functions. The "machine center" will perform such procedures as milling, drilling, boring, tapping and others sometimes with the requirment that guards be actuated or safety doors be opened and closed, and loading and unloading of stock and tool components be carried out. Maintenance down time necessarily is a factor in the operation of all such machine tools whether automated or otherwise. While these various devices, arrayed in a machine shop environment prove effective in the production of most piece part designs, their efficiencies as reflected in the cost of each part diminish as different types or configurations of parts are required to be produced.
Efforts to automate the manufacture of piece parts as well as to carry out assembly procedures and the like have taken diverse technical approaches, determined principally by the numbers of items called for in the production process. Where the part design remains consistent and the numbers called for are, in effect, of great extent, a wider selection of automated but somewhat dedicated aproaches becomes available to the plant designer. However, as the parts requiring machining change in design and lower volume "batch" production is called for, manufacturing efficiencies become more elusive to achieve. Anticipated by some investigators as to account for as much as 75% of production, batch manufacturing is considered to be labor intensive, involving machining operations which traditionally are slower due to required operator attention. See in this regard: Holmes, "Justifying a Robot Machining System in Batch Manufacturing," Robotics Today, p. 86, 182, Annual Edition Robotics International, S.M.E., Dearborn, Mich. 48128. Batch production consists of a relatively high part mix and low individual part volumes. Where machines in the shop are arranged functinally for these procedures, high in-process inventory and long lead times typically are encountered. Customized automated systems are not applicable for such batch manufacturing, inasmuch as they prove too costly. Resort necessarily has been made to providing some automation of available standards machines and assemblers already in the shop inventor of the fabricator.
A modicum of improvement in batch manufacturing productivity has been accomplished with the introduction of computer numerical control (CNC) machine tools, machine centers, group technology, tool management, and robot piece-part feeding systems. Thus far, flowline designs for manufacturing systems have been hindered somewhat by available feeding approaches. For example, palletization often has been considered as an essential aspect of feed procedure. However, such palletization techniques often preclude necessary machinery procedures such as turning, an often called for activity.
The above limitations have been seen to restrict localized automation suited for batch scale production. Robots have been employed to "pick and put" piece parts into and out of machines in batch-type production installations sometimes referred to as "flexible machine systems" (FMS). Movement of parts from one machine to the next in the FMS production flow sequence has been carried out, for example, on an automated and larger scale basis by gantry supported robots. These rectilinear systems necessarily require a somewhat extensive amount of plant floor space and have practical limitations with respect to throughput rates, i.e. they are not high volume systems. For example, the extent of travel of the robots by gantry movement necessarily is limited by machine cycle considerations, i.e. the robot being required to return and feed an initial production stage of a given section of the system on a cyclical basis. As an example of travel time limitations, a gantry carried robot may feed a first or head machine, then commence to travel down the gantry bay to carry out subsequent machine servicing operations. However, the extent of this travel is limited by the part cycle of the first machine. If that part cycle, for example is three minutes, then a corresponding limitation is placed upon the available servicing region of the process starting robot. As a result, additional robots and supporting movable gantry bridges must be employed in the production line which, in further consequence, becomes longer requiring more and more plant space. However, the gantry robot systems do achieve the advantage of process flexibility using conventional machine stages.
Additional considerations which enter into the design of batch-type production systems include requirement for part control and storage at machine inputs. Realistically, the cycle times of machines will differ from stage to stage in a production process flow and, as a consequence, queying of piece parts at the inputs to machine stages becomes the norm, zones of piece parts at the inputs to machine stages becomes the norm, zones of piece part storage or stand-by retention usually being required throughout the production process path. As a consequence, higher in-process inventory levels are necessitated. Requisite storage zones also call for expanded plant space allocation for a given flexble machine system, to contribute further to production overhead costs. Downtime for machine maintenance and repair also is a process design consideration. Where a given stage in the production flow path is down, then surges in piece part may be anticipated and storage banks or zones must be designed to handle worse case surge conditions. Such zonal requirement may become extensive where surges amounting, for example, up to 1,000 parts can be anticipated.
While robots hold out promise for achieving automation in batch level production operations, their use for that purpose thus far has been inadequate in terms of efficiency. The latter inadequacies stem principally form station-to-station travel time limitations, piece-part storage requirements, limited service, access to machines during their operation (a typical machine experiences 10% downtimes), and extended plant floor space requirements. It is necessary that, for any given production facility, the use of individual robots be maximized, thus lowering the number of such devices required to perform the function of the facility.